1. Field of the Invention
The present invention relates to a photoresist used in photolithography, and treatment techniques of the resist.
2. Related Background Art
There is no end to the pursuit of higher integration density of micro devices such as semiconductor devices, and processing applying the photolithography technology is demanded to achieve further finer patterning. Light sources used in exposure apparatus are thus switching from the conventional i-line light sources such as a mercury lamp to KrF and ArF excimer laser light sources of shorter wavelengths. Further, chemical amplification type resists with higher resolution are drawing attention as resists used in that case.
However, because the excimer laser light has very high irradiation energy, there is a possibility of taking place a reaction of a base resin itself, which did not take place with the conventional i-line. For example, in the case of the KrF excimer laser, novolak or polyvinyl phenol, used as a base resin of a resist, is oxidized by exposure to the KrF excimer laser. In more detail, activation energy of oxidation of the phenol is about 2.8.times.10.sup.-20 (J), while energy (h.nu.) of the KrF excimer laser is 8.01.times.10.sup.-19 (J). This thus explains why the energy of the excimer laser causes the oxidation.
Quinones produced by this oxidation have absorption at wavelengths near 300 nm, and thus decrease the transmittance in the wavelength region of the KrF excimer laser. The decrease of transmittance will raise the problem that an adequate profile cannot be achieved when the resist is developed.
Further, the oxidation of the base resin will result in changing the dissolving rate thereof into a developer, which, in turn, will raise problems of changing the sensitivity and changing the resist line width transferred.